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title	description	slug	section
DIDs & DDOs - Asset Identifiers & Objects	Specification of Ocean asset identifiers and objects using DIDs & DDOs	/concepts/did-ddo/	concepts

Overview

This document describes how Ocean assets follow the DID/DDO spec, such that Ocean assets can inherit DID/DDO benefits and enhance interoperability.

Decentralized identifiers (DIDs) are a new type of identifier that enables verifiable, decentralized digital identity. Each DID is associated with a unique entity. DIDs may represent humans, objects, and more.

A DID Document (DDO) is JSON blob that holds information about the DID. Given a DID, a resolver will return the DDO of that DID.

If a DID is the index key in a key-value pair, then the DID Document is the value to which the index key points. The combination of a DID and its associated DID Document forms the root record for a decentralized identifier.

DIDs and DDOs follow the specification defined by the World Wide Web Consortium (W3C).

Rules for DIDs & DDOs in Ocean

An asset in Ocean represents a downloadable file, compute service, or similar. Each asset is a resource under control of a publisher. The Ocean network itself does not store the actual resource (e.g. files).

An asset should have a DID and DDO. and the DDO should include metadata about the asset. The DDO can only can be modified by owners or delegated users.

There must be at least one client library acting as resolver, to get a DDO from a DID. A metadata cache like Aquarius can help in reading and searching through DDO data from the chain.

State

Each asset has a state, which is held by the NFT contract. The possible states are:

0 = active
1 = end-of-life
2 = deprecated (by another asset)
3 = revoked by publisher

Publishing an Retrieving DDOs

The DDO is stored on-chain as part of the NFT contract and it is stored encrypted using the private key of the Provider. To resolve it, a metadata cache like Aquarius must query the provider to decrypt the DDO.

Here is the complete flow:

title DDO flow

User(Ocean library) -> User(Ocean library): Prepare DDO
User(Ocean library) -> Provider: encrypt DDO
Provider -> User(Ocean library): encryptedDDO
User(Ocean library) -> ERC721 contract: publish encryptedDDO
Aquarius <-> ERC721 contract: monitors ERC721 contract and gets MetdadataCreated Event (contains encryptedDDO)
Aquarius -> ERC721 contract: calls getMetaData()
Aquarius -> Provider: decrypt encryptedDDO, signed request using Aquarius's private key
Provider -> ERC721 contract: checks state using getMetaData()
Provider -> Provider: depending on metadataState (expired,retired) and aquarius address, validates the request
Provider -> Aquarius: DDO
Aquarius -> Aquarius : validate DDO
Aquarius -> Aquarius : cache DDO
Aquarius -> Aquarius : enhance cached DDO in response with additional infos like `events` & `stats`

DID Structure

In Ocean, a DID is a string that looks like:

did:op:0ebed8226ada17fde24b6bf2b95d27f8f05fcce09139ff5cec31f6d81a7cd2ea

where

0ebed8226ada17fde24b6bf2b95d27f8f05fcce09139ff5cec31f6d81a7cd2ea` = sha256(ERC721 contract address + chainId)

It follows the generic DID scheme.

DDO Attributes

A DDO has these required attributes:

@context = array, contexts used for validation
id = string, computed as sha256(address of ERC721 contract + chainId)
created = contains the date of publishing, ISO Date Time Format yyyy-MM-dd'T'HH:mm:ss. SSSXXX — for example, "2000-10-31T01:30:00.000-05:00
updated = contains the date of last update, ISO Date Time Format

In Ocean, the DDO also has:

version - string, stores version information (example: v4.0.0)
chainId - integer, stores chainId of the network used
metadata - stores metadata information Metadata
services - stores an array of services Services
credentials - optional flag, which describes the credentials needed to access a dataset Credentials
files and encryptedFiles - stores file(s) informations Files

In addition, Aquarius will add the following objects, which are not taken into account when DDO hash is calculated:

status - stores status related fields Status
event - stores the last event information Event
stats - stores several fields for statistics Stats

Metadata

The object has the following attributes.

Attribute	Type	Required	Description
`description`	Text	Yes	Details of what the resource is. For a dataset, this attribute explains what the data represents and what it can be used for.
`copyrightHolder`	Text	No	The party holding the legal copyright. Empty by default.
`name`	Text	Yes	Descriptive name or title of the asset.
`type`	Text	Yes	Asset type. Includes `"dataset"` (e.g. csv file), `"algorithm"` (e.g. Python script). Each type needs a different subset of metadata attributes.
`author`	Text	Yes	Name of the entity generating this data (e.g. Tfl, Disney Corp, etc.).
`license`	Text	Yes	Short name referencing the license of the asset (e.g. Public Domain, CC-0, CC-BY, No License Specified, etc. ). If it's not specified, the following value will be added: "No License Specified".
`links`	Array of Link	No	Mapping of links for data samples, or links to find out more information. Links may be to either a URL or another Asset. We expect marketplaces to converge on agreements of typical formats for linked data: The Ocean Protocol itself does not mandate any specific formats as these requirements are likely to be domain-specific. The links array can be an empty array, but if there is a link object in it, then an "url" is required in that link object.
`contentLanguage`	Text	No	The language of the content. Please use one of the language codes from the IETF BCP 47 standard
`categories`	Array of Text	No	Optional array of categories associated to the asset. Note: recommended to use `"tags"` instead of this.
`tags`	Array of Text	No	Array of keywords or tags used to describe this content. Empty by default.
`additionalInformation`	Object	No	Stores additional information, this is customizable by publisher

Depending on the asset type (dataset, algorithm), there are different metadata attributes supported:

Algorithm attributes

An asset of type algorithm has the following additional attributes under algorithm in metadata object:

Attribute	Type	Required	Description
`language`	`string`	no	Language used to implement the software
`version`	`string`	no	Version of the software.
`container`	`Container Object`	yes	Object describing the Docker container image.(see below)

The container object has the following attributes:

Attribute	Type	Required	Description
`entrypoint`	`string`	yes	The command to execute, or script to run inside the Docker image.
`image`	`string`	yes	Name of the Docker image.
`tag`	`string`	yes	Tag of the Docker image.
`checksum`	`string`	yes	Checksum of the Docker image.

Services

Attribute	Type	Required	Description
`type`	Text	Yes	Type of service (access, compute, wss, etc
`name`	Text	No	Service friendly name
`description`	Text	No	Service description
`datatokenAddress`	Text	Yes	Datatoken address
`providerEndpoint`	Text	Yes	Provider URI
`timeout`	Number	Yes	describing how long the sevice can be used after consumption is initiated. A timeout of 0 represents no time limit. Expressed in seconds.
`files`	Array of files object	No	Array of `File` objects including the encrypted file urls that overwrites the root files object for this service Files

Depending on the service type, the following attributes are applied:

Compute datasets attributes

An asset with a service of type compute has the following additional attributes under privacy object :

Attribute	Type	Required	Description
`allowRawAlgorithm`	`boolean`	yes	If True, a drag & drop algo can be runned
`allowNetworkAccess`	`boolean`	yes	If True, the algo job will have network access (stil WIP)
`publisherTrustedAlgorithmPublishers`	Array of `String`	yes	If Empty , then any published algo is allowed. Otherwise, only published algorithms by some publishers are allowed
`publisherTrustedAlgorithms`	Array of `publisherTrustedAlgorithms`	yes	If Empty , then any published algo is allowed. (see below)

The publisherTrustedAlgorithms is an array of objects with the following structure:

Attribute	Type	Required	Description
`did`	`string`	yes	The did of the algo which is trusted by the publisher.
`filesChecksum`	`string`	yes	Hash of ( algorithm's encryptedFiles + files section (as string) )
`containerSectionChecksum`	`string`	yes	Hash of the algorithm container section (as string)

To produce filesChecksum:

sha256(
  algorithm_ddo.service['metadata'].attributes.encryptedFiles +
    JSON.Stringify(algorithm_ddo.service['metadata'].attributes.main.files)
)

To produce containerSectionChecksum:

sha256(
  JSON.Stringify(
    algorithm_ddo.service['metadata'].attributes.main.algorithm.container
  )
)

Example:


{
   {...},
   "services":[
      {
         "type":"access",
         "name":"Download service",
         "description":"Download service",
         "datatokenAddress":"0x123",
         "providerEndpoint":"https://myprovider",
         "timeout":0
      },
      {
         "type":"compute",
         "name":"Compute service",
         "description":"Compute service",
         "datatokenAddress":"0x124",
         "providerEndpoint":"https://myprovider",
         "timeout":0,
         "privacy":{
            "allowRawAlgorithm":false,
            "allowNetworkAccess":true,
            "publisherTrustedAlgorithmPublishers":[
               "0x234",
               "0x235"
            ],
            "publisherTrustedAlgorithms":[
               {
                  "did":"did:op:123",
                  "filesChecksum":"100",
                  "containerSectionChecksum":"200"
               },
               {
                  "did":"did:op:124",
                  "filesChecksum":"110",
                  "containerSectionChecksum":"210"
               }
            ]
         }
      }
   ]
}

Credentials

By default, a consumer can access a resource if they have 1.0 datatokens. Credentials allow the publisher to optionally specify finer-grained permissions.

Consider a medical data use case, where only a credentialed EU researcher can legally access a given dataset. Ocean supports this as follows: a consumer can only access the resource if they have 1.0 datatokens and one of the specified "allow" credentials.

This is like going to an R-rated movie, where you can only get in if you show both your movie ticket (datatoken) and some some id showing you're old enough (credential).

Only credentials that can be proven are supported. This includes Ethereum public addresses, and (in the future) W3C Verifiable Credentials and more.

Ocean also supports "deny" credentials: if a consumer has any of these credentials, they cannot access the resource.

Here's an example object with both "allow" and "deny" entries.

{
  {...},
  "credentials":{
      "allow":[
         {
            "type":"address",
            "values":[
               "0x123",
               "0x456"
            ]
         }
      ],
      "deny":[
         {
         "type":"address",
         "values":[
            "0x2222",
            "0x333"
         ]
         }
      ]
  }
}

For future usage, we can extend that with different credentials types. Example:

{
  "type": "credential3Box",
  "values": ["profile1", "profile2"]
}

Files

The files section contains a file object (that contains a list of file objects) and a encryptedFiles string which contains the encrypted urls

Each file object has the following attributes, with the details necessary to consume and validate the data.

Attribute	Required	Description
`contentType`	Yes	File format.
`url`	Local	Content URL. Omitted from the remote metadata. Supports `http(s)://` and `ipfs://` URLs.
`name`	No	File name.
`checksum`	No	Checksum of the file using your preferred format (i.e. MD5). Format specified in `checksumType`. If it's not provided can't be validated if the file was not modified after registering.
`checksumType`	No	Format of the provided checksum. Can vary according to server (i.e Amazon vs. Azure)
`contentLength`	No	Size of the file in bytes.
`encoding`	No	File encoding (e.g. UTF-8).
`compression`	No	File compression (e.g. no, gzip, bzip2, etc).
`encrypted`	No	Boolean. Is the file encrypted? If is not set is assumed the file is not encrypted
`encryptionMode`	No	Encryption mode used. Just valid if `encrypted=true`
`resourceId`	No	Remote identifier of the file in the external provider. It is typically the remote id in the cloud provider.
`attributes`	No	Key-Value hash map with additional attributes describing the asset file. It could include details like the Amazon S3 bucket, region, etc.

Example:

{
  {..},
  files:{
    "files": [
            {
              "contentLength": "3975",
              "contentType": "text/csv"
            }
          ],
    "encryptedFiles": "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",
  }
}

DDO Hash

In order to ensure the integrity, a hash is computed for each DDO:

const hash = sha256(JSON.stringify(DDO))

The hash is used when publishing/update metadata using setMetaData function in ERC721 contract and it is stored in the event generated by the ERC721 contract:

event MetadataCreated(
       address indexed createdBy,
       uint8 state,
       string decryptorUrl,
       bytes flags,
       bytes data,
       bytes metaDataHash,
       uint256 timestamp,
       uint256 blockNumber
   );

event MetadataUpdated(
       address indexed updatedBy,
       uint8 state,
       string decryptorUrl,
       bytes flags,
       bytes data,
       bytes metaDataHash,
       uint256 timestamp,
       uint256 blockNumber
   );

Aquarius should always check the hash after data is decrypted via a Provider API call, in order to ensure DDO integrity.

Aquarius Enhanced DDO Response

The following fields are added by Aquarius in its DDO response for convenience reasons. These are never stored on chain, and not taken into consideration when hashing the DDO.

Status

The status object contains the following attributes:

Attribute	Type	Required	Description
`state`	`number`	yes	State of the asset reflecting the NFT contract value. See State
`isListed`	`boolean`	no	If this asset should be displayed
`isOrderDisabled`	`boolean`	no	If this asset has ordering disabled

{
  {...},
  "status": {
    "state": 0,
    "isListed": true,
    "isOrderDisabled": false
  }

Events

The events section contains informations about the transactions that created or updated the DDO

{
  {...},
  "events": [{
    "txid": "0x8d127de58509be5dfac600792ad24cc9164921571d168bff2f123c7f1cb4b11c",
    "blockNo": 12831214,
    "from": "0xAcca11dbeD4F863Bb3bC2336D3CE5BAC52aa1f83",
    "contract": "0x1a4b70d8c9DcA47cD6D0Fb3c52BB8634CA1C0Fdf",
    "update": false,
    "chainId": 1,
  }]

Stats

The stats section contains different statics fields.

{
  {...},
  "stats": {
    "consumes":4
  }

Full Enhanced DDO Example:

{
  "@context": ["https://w3id.org/did/v1"],
  "id": "did:op:ACce67694eD2848dd683c651Dab7Af823b7dd123",
  "created": "2020-11-15T12:27:48Z",
  "updated": "2021-05-17T21:58:02Z",
  "version": "v4.0.0",
  "chainId": 1,
  "metadata": {
    "description": "Sample description",
    "name": "Sample asset",
    "type": "dataset",
    "author": "OPF",
    "license": "https://market.oceanprotocol.com/terms"
  },
  "files": {
    "files": [
      {
        "url": "https://demo.com/file.csv"
      }
    ],
    "encryptedFiles": "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"
  },
  "services": [
    {
      "type": "access",
      "name": "Download service",
      "description": "Download service",
      "datatokenAddress": "0x123",
      "providerEndpoint": "https://myprovider",
      "timeout": 0
    }
  ],
  "credentials": {
    "allow": [
      {
        "type": "address",
        "values": ["0x123", "0x456"]
      }
    ],
    "deny": [
      {
        "type": "address",
        "values": ["0x2222", "0x333"]
      }
    ]
  },

  // Enhanced Aquarius response begins here
  "status": {
    "state": 0,
    "isListed": true,
    "isOrderDisabled": false
  },
  "events": [
    {
      "txid": "0x8d127de58509be5dfac600792ad24cc9164921571d168bff2f123c7f1cb4b11c",
      "blockNo": 12831214,
      "from": "0xAcca11dbeD4F863Bb3bC2336D3CE5BAC52aa1f83",
      "contract": "0x1a4b70d8c9DcA47cD6D0Fb3c52BB8634CA1C0Fdf",
      "update": false,
      "chainId": 1
    }
  ],
  "stats": {
    "consumes": 4
  }
}

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